1. Field of the Invention
The present invention relates to a sensor for detecting a rotational movement or an angular acceleration, and in particular to a sensor for detecting a rotational movement or an angular acceleration which comprises a heating element and a sensor element.
2. Description of the Prior Art
DE 42 43 978 C1 describes a tilt and acceleration sensor comprising in a closed, fluid-filled housing a sensor structure which includes at least two temperature-dependent electric resistors, at least one of the resistors being heated. The convective flow occurring in a gravity or inertia field in the fluid within the housing is evaluated and the signals, which are detected by the sensor, are directly related to the tilt angle and to the acceleration of the sensor system.
EP 95 300 345.6 describes a sensor including at least one temperature-detecting resistance means which is arranged in the interior of a closed space. A gas contained in the closed space is heated and, when a acceleration acts on the sensor, the resistance of the resistance means changes due to the flow of the heated gas across the resistance means. The sensor comprises a semiconductor or an insulating substrate having a cavity provided therein, and a projecting means made of an insulating material and extending in the space at least partially transversely to the cavity, the resistance means being formed integrally with the projecting means.
U.S. Pat. No. 4,361,054 describes an arrangement of hot-wire air velocity meters which are partly installed in a rotor boundary layer so that they form two resistors of a Wheatstone bridge circuit for each axis. The hot-wire resistors change their resistance values in accordance with the angular displacement of the gyrorotor relative to zero. The combination of the resistance changes is then used in the bridge circuit so as to provide an electric signal which is directly proportional to an angular displacement of the gyrorotor.
U.S. Pat. No. 4,020,700 describes a rotary speed sensor which samples by means of hot-wire probes a fluid flow produced by a pump. The nozzle of the rotary speed sensor, which directs a fluid towards a pair of temperature-dependent detection resistance elements, is formed in a main block defining a chamber in which also the detection elements are provided, whereby problems of aligning the jet with respect to the chamber and problems of aligning the detection elements with respect to the nozzle are reduced.
U.S. Pat. No. 5,780,738 describes a device for detecting a rotary speed rate which comprises a body defining a surface with a projecting portion and an opening through the surface, the opening being located in the vicinity of the projecting portion and a fluid flow being directed through this opening along an initial flow axis. The projecting portion orients the fluid flow into a path along the surface in accordance with the Coanda effect. A first flow sensor is secured in position relative to the body and in the vicinity of the path of the fluid flow along the surface of the body. The first flow sensor produces a first indication of a flow rate of a first section of the fluid flow in the vicinity thereof. A second flow sensor is secured in position relative to the body and in the vicinity of the path of the fluid flow along the surface of the body. The second flow sensor produces a second indication of a flow rate of a second section of the fluid flow in the vicinity thereof. The rotary movement of the body is detected in dependence upon the first indication and the second indication.
EP 0 328 247 B1 describes an angular velocity sensor producing an output signal when there is a difference between the output signals of a pair of heat sensors in cases in which, due to the influence of a movement imparted to the gas stream and having the angular velocity to be determined impressed thereon, the gas stream discharged from a gas nozzle sweeps over one of the heat sensors more strongly than over the other.
EP 0 786 645 A2 describes a sensor for detecting a rotary speed rate or an angular acceleration with the aid of a capacitive evaluation of from 2 to 4 moving, i.e. vibrating mass paddles, the sensor being implemented in microsystem technology. The sensor for detecting the rotary speed rate or the angular acceleration includes a vibrator comprising at least two vibrating masses and beams for supporting these masses. The vibrator is formed making use of a monocrystal silicon substrate of the (110)-crystal plane, and the two beams use as main planes two kinds of (111)-crystal planes, which are perpendicular to the silicon substrate and which do not extend parallel to one another; the two beams are flexible in a direction which is parallel to the silicon substrate and vertical to each of the (111)-crystal planes. Capacitance changes between the masses and a group of electrodes are detected.
In addition, rotary speed sensors are known in the case of which the capacitive change of moving masses relative to a fixed mass is evaluated for the purpose of determining the rotary speed.
One disadvantage of known methods and sensors for detecting a rotational movement or an angular acceleration is that these methods and sensors use e.g. moving masses which necessitate the use of a sensitive suspension.
A further disadvantage of known methods and sensors for detecting a rotational movement or an angular acceleration is that these sensors require a complicated structural design which entails a high expenditure and high costs.
Another disadvantage of known methods and sensors for detecting a rotational movement or an angular acceleration is that, e.g. in the case of sensors for detecting a fluid flow, it will be necessary to use devices for producing a fluid flow, such as a pump, so that the fluid flow can be measured.
It is the object of the present invention to provide a sensor for detecting a rotational movement or an angular acceleration, which has a simple and robust structural design.
The present invention is a sensor for detecting a rotational movement, an angular acceleration, a tilt or an acceleration, having at least one heating element which is arranged in a first plane extending at right angles to an axis of rotation, the heating element being adapted to produce in a fluid surrounding the heating element a convection flow zone through which an isothermal field is defined; and at least one sensor element, the fluid surrounding the sensor element, and the sensor element being adapted to be displaced relative to the isothermal field when a rotational movement or an angular acceleration takes place, wherein the heating element extends in the form of a circular arc or in form of an interrupted polygonal progression around the axis of rotation.
The present invention is based on the finding that the inertia of a locally heated fluid can be utilized for detecting a rotational movement or an angular acceleration. For this purpose, the fluid is heated in a local area by means of a heating element to a certain temperature and, by means of a rotational movement, the locally heated area and the heating element are moved relative to one another so that the locally heated area of the fluid will move e.g. towards a sensor element located adjacent the heating element, whereby the sensor element will detect a change in the temperature of the fluid and, consequently, a movement. For detecting a rotational movement or an angular acceleration, the heating element and the sensor element are preferably located on a common circle around the axis of rotation of the rotational movement or of the angular acceleration.
One advantage of the sensor according to the present invention is that it is robust, over-load-proof and capable of operating in any position and that it does not have any movable mass elements.
A further advantage of the sensor according to the present invention is that it is capable of carrying out self-tests.
Yet another advantage of the sensor according to the present invention is that it is suitable for modern mass production methods, e.g. in the field of microsystem technology and semiconductor production lines, and that it can be produced at a moderate price.